Introduction

Caffeine is a naturally occurring drug found in more than 60 plant species. It stimulates the central nervous system and may temporarily increase alertness and relieve fatigue. Caffeine is found in a range of popular foods and beverages including coffee, tea, chocolate, cola flavoured soft drinks and energy drinks. Some medicines also contain caffeine.

Caffeine is the most commonly consumedpsychoactive (affecting the mind or mood) drug globally. When consumed in moderation caffeine does not appear to have adverse health affects but excessive consumption poses health risks.

From which foods and beverages do adults consume caffeine?

Australian statistics are limited, but as a guide, adults in Canada obtain some 60% of their caffeine from coffee, 30% from tea and the remaining 10% from a combination of chocolate, cola beverages and medications.

How much caffeine can adults safely consume?

Humans have no nutritional requirement for caffeine and their health will not suffer if they do not consume any caffeine. However, caffeine can be consumed safely by humans, provided it is consumed in moderation. Research shows that most adults can consume up to 400mg of caffeine per day, without negatively affecting their health in terms of:

Recommendations for caffeine intake

In Australia, it is recommended that individuals consume no more than 600mg of caffeine per day in order to avoid health risks. However, recommendations regarding how much caffeine an individual should consume vary from country to country. For example, in the United States health authorities recommend adults consume no more than 250mg of caffeine per day, while in Canada up to 400mg per day is considered safe for adults.

Some adults may be more sensitive to the effects of caffeine and need to consume less caffeine or avoid caffeine intake altogether in order to protect their health and wellbeing, including:

Individuals with cardiovascular disorders or risk factors such as high blood pressure. This is because caffeine increases cardiac risk factors including blood pressure and homocysteine (an amino acid found in blood, high concentrations of which are associated with cardiovascular disorders); and

Children.

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Caffeine overdose

Caffeine overdose is rare and occurs in adults following consumption of >5-10mg of caffeine (equivalent to drinking about 80 cups of strong coffee in a row). However, symptoms of toxicity (poisoning) may occur with lower doses and include:

Health effects associated with excessive caffeine consumption

Physical

Short term effects

Excessive caffeine consumption is associated with numerous short term physical health effects including:

Temporary changes to the heart – including increased heart rate, heart arrhythmia (abnormal heart rhythm) andincreased blood pressure. It should be noted that these temporary changes have not been shown to increase the risk of long term cardiac disorders such as coronary heart disease and irregular heartbeat (atrial fibrillation);

Excessive urination due to the diuretic effect of caffeine. It causes the kidneys to produce more urine and may in turn lead to dehydration, and increase the loss of dietary minerals including calcium, as these minerals are excreted from the body in urine;

Nausea and vomiting;

Increased secretion of gastric acids;

Muscle tremors (involuntary muscle movements); and

Insomnia (inability to sleep).

The exact amount of caffeine required to produce these effects varies from person to person, as individual bodies tolerate caffeine differently and some are more sensitive to its effects. Some individuals require only a small amount of caffeine (e.g. a cup of coffee) to produce these effects. Others, and particularly those who consume caffeine regularly, are less sensitive to its effects.

Appetite suppression

Caffeine is an appetite suppressant and individuals who consume excessive amounts of caffeine may eat less. Caffeine containing beverages may also replace more healthy alternatives including milk, water and juice.

Bone mineral density in women

Caffeine is a diuretic which increases urinary output and the excretion of calcium and other minerals, which may affect bone mineral density. However, the association between bone mineral loss and caffeine consumption remain inconclusive. Some studies have found associations between caffeine consumption and bone mineral loss, while others have not.

Other studies have found that the association between caffeine and bone mineral density depends on a woman’s overall calcium intake. For example, one early study found that post-menopausal women with low calcium and high caffeine consumption had significantly reduced bone mineral density, but women who consumed the recommended daily intake of calcium (800mg) did not have reduced bone mineral density if they consumed a lot of caffeine. However, other studies indicate that excessive caffeine consumption may also negatively affect bone mineral density in women who consume adequate amounts of calcium.

A woman’s history of oral contraceptive use and genetic factors may also influence the associations between caffeine intake and bone mineral density. One study showed that oral contraceptive use significantly reduced the amount of calcium lost through urination following caffeine consumption. The results of the study suggest that oral contraceptive use may protect against reduced bone mineral density arising from high caffeine consumption.

Another study reported that all post-menopausal women with caffeine consumption >300mg per day had significantly greater bone mineral loss compared to those consuming ≤300mg per day. However genetic factors, specifically genetic differences in the way in which the body processes vitamin D, influenced the severity of bone mineral loss.

Psychological

The effects of excessive caffeine consumption may mimic those of psychological disorders including anxiety, sleep and eating disorders. Doctors are therefore likely to ask an individual about their caffeine intake, if they present with an anxiety or sleep disorder.

Caffeine is a stimulant and its sleep disturbing effects are well documented. It reduces both slow wave sleep (in the early part of the sleep cycle) and rapid eye movement sleep (deep sleep in the later part of the cycle). Caffeine consumption increases periods of wakefulness, the time it takes an individual to fall asleep and difficulty individuals have falling asleep.

While research evidence is limited, some doctors report that individuals with eating disorders may consume excessive caffeine in the belief that it will stimulate their metabolism and/or suppress their appetite and assist weight loss.

Sexual

There is also some evidence that caffeine consumption affects aspects of sexual and reproductive health for both men and women.

In vitro fertilisation outcomes

Caffeine consumption has been shown to reduce the likelihood of successful outcomes following assisted reproductive treatments, including in vitro fertilisation.

Pregnancy outcomes

Excessive caffeine intake may also negatively affect foetal development and pregnancy outcomes.

Excessive caffeine consumption during breastfeeding may have negative affects for the baby being breastfed.

More information on caffeine and breastfeeding

Health effects not associated with caffeine consumption

Cardiovascular disease

Initial evidence from research studies suggested that excessive caffeine intake may adversely affect the cardiovascular system and increase an individual’s risk of cardiovascular disorders. However, later studies suggest that there is no association between excessive caffeine consumption and cardiovascular disorders. The American Heart Foundation has concluded that there is currently insufficient evidence to determine whether or not excessive caffeine consumption increases the risk of coronary heart disease.

There have been very rare cases of death associated with very high caffeine intake by individuals with existing heart disorders, but most individuals can tolerate moderate amounts of caffeine. Evidence demonstrates no association between caffeine consumption and an increased risk of atrial fibrillation, and most studies have not found an increased risk of coronary heart disease. However, caffeine consumption is associated with increased blood pressure and homocysteine, which are risk factors for cardiovascular disease. Because of these effects it is recommended that individuals with cardiac disorders or risk factors for developing cardiac disorders limit their caffeine intake.

Gastro-oesophageal reflux disease

Caffeine affects the gastrointestinal system and numerous studies of the associations between caffeine consumption and gastro-oesophageal reflux disease (GORD) have been conducted. However, results are conflicting and there is currently insufficient evidence to determine whether or not caffeine intake influences an individual’s risk of developing this disease.

Infertility

Research investigating the effects of caffeine consumption on fertility is limited. Current evidence is inconsistent, meaning that some studies indicate caffeine consumption reduces fertility, while others do not. As such there is insufficient evidence to suggest an association between caffeine consumption and reduced fertility. However, there is some evidence that combined smoking and caffeine consumption negatively affects sperm health.

Fibrocystic breast disease

While early uncontrolled studies linked caffeine consumption to fibrocystic breast disease (a condition characterised by non-cancerous lumps in the breasts), later studies indicate caffeine does not play a causative role in the development of this common disease.

Health benefits associated with caffeine consumption

Consuming caffeine can provide short term relief from fatigue and drowsiness. It may also increase alertness and improve an individual’s mood. However, it is important to note that individuals who consume large amounts of caffeine to relieve short-term fatigue (e.g. to allow them to stay up studying late at night) may feel tired and lethargic the following day.

Type 2 diabetes mellitus

Of 17 studies conducted, 14 showed that caffeine consumption lowers the risk of type 2 diabetes mellitus amongst both men and women, obese and non-obese individuals. Many of the studies, which have been conducted amongst a range of ethnic groups, have found a dose-response relationship, meaning that the more caffeine and individual consumed, the less likely they were to develop diabetes. In addition, caffeine intake has been shown to reduce insulin sensitivity in the short term. However, this is not an indicator to start consuming greater quantities of caffeine.

Stroke

Data from the Nurses Health Study suggest that caffeine consumption reduces the risk of stroke in women.

Moderate caffeine consumption reduces the risk of Parkinson’s disease in women who do not use hormone replacement therapy, but increases the risk in those who take post-menopausal hormones. Women with high caffeine intake who use hormones are almost 4 times more likely to develop Parkinson’s disease.

Reducing caffeine consumption

Individuals who consume too much caffeine (>600mg daily) should attempt to reduce their caffeine intake. The best approach is to reduce caffeine intake gradually, for example by replacing one caffeinated drink with one non-caffeinated drink each day. This will reduce the likelihood of withdrawal symptoms, which may occur if caffeine is eliminated completely from the diet.

Individuals who have heart problems, take medications that interact with caffeine or women who may become pregnant should also consider reducing their caffeine intake, even if they consume

More information

For more information on caffeine, including consumption by adults, children and pregnant women, as well as some useful tools, see Caffeine.

For more information on nutrition, including information on types and composition of food, nutrition and people, conditions related to nutrition, and diets and recipes, as well as some useful videos and tools, see Nutrition.

National Drug and Alcohol Research Centre- University of New South Wales. Caffeine- fact sheet. 2001. [cited 2010, June 30]. Available from: http://ndarc.med.unsw.edu.au/NDARCWeb.nsf/resources/NDARCFact_Drugs6/$file/caffeine+fact+sheet.pdf

Royal College of Obstetricians and Gynaecologists. Fertility: assessment and treatment for people with fertility problems. 2004. [cited 2010, June 29]. Available from: http://www.rcog.org.uk/womens-health/clinical-guidance/fertility-assessment-and-treatment-people-fertility-problems.